1. Field of the Invention
The invention is directed to a vibration damper with stroke-dependent damping force.
2. Description of the Related Art
A general problem in conventional vibration dampers is the spectrum between the smallest, softest damping force and the largest, hardest damping force. Particularly in a vehicle that is only slightly loaded, the damping force is often too great because a loaded vehicle must also still be reliably controllable. In order to resolve this conflict, it has been well known for a long time to use vibration dampers with elongated grooves in the work cylinder. With less of a load, the damping medium can flow around a piston at a piston rod via a bypass and, in this way, can bring about a reduction in the damping force. However, the result that can be achieved is still not always satisfactory.
It is disclosed in DE 103 43 875 A1 that an appreciably greater range of damping force can be achieved by adding an additional pressure-actuated surface to a damping valve via the bypass groove in the work cylinder. The bypass groove serves to supply damping medium to the pressure-actuated surface at a valve disk. Inflow is blocked outside the bypass groove so that there is only one surface available at the valve disk that is continuously subject to incident flow and the damping force is defined in this way. This damping valve construction basically allows three levels of damping force. When the piston ring 11 is located outside the bypass groove 49, the vibration damper operates at the highest damping force setting. When the piston ring 11 moves inside the bypass groove, but the seal 45 moves outside the bypass groove, then a softer damping force setting is available by the inflow to the additional pressure-actuated surface at the valve disk. The softest damping force setting is achieved when both the piston ring 11 and the seal 45 are located inside the bypass groove 49.